Slow movers opt for a single sex

Biologists have long assumed that whether a species evolved to have separate males and females or to combine both in a single individual has a lot to do with an organism’s mobility. Slow-moving animals are unlikely to encounter many prospective mates and thus should be hermaphrodites to maximise their mating opportunities – if all else fails they can mate with themselves. But more wide-ranging species can afford to have separate sexes, allowing them to enjoy the benefits of outcrossing, mixing their genes with unrelated individuals. …